The invention generally relates to converting video and image signal bit depths.
Modern display devices (computer monitors, televisions, mobile device screens, etc.) have ever increasing abilities to display images that have relatively high dynamic ranges. In general, an image that has a relatively higher dynamic range has more bits per pixel value, called the “bit depth,” than an image that has a relatively lower dynamic range.
A video signal may have a lower associated bit depth than the maximum bit depth capability of a given display device. Therefore, the video signal may be processed to produce another video signal that has a higher bit depth for purposes of driving the display device. One traditional approach for converting bit depth involves tone mapping. In general, tone mapping includes linear scaling, piecewise interpolation and table look-up techniques to specify the per pixel mapping between the low and high bit depth video signals.
A video encoder that generates the low bit depth video signal typically generates additional tone mapping data (such as look-up table data) that describes the tone mapping, and at the display device end, a video decoder receives this additional tone mapping data along with the low bit depth video signal. The video decoder typically constructs the high bit depth signal from the low bit depth signal according to the accompanying tone mapping data. A particular challenge associated with the above-described tone mapping approach is that transmission bandwidth and/or storage bandwidth may be consumed for purposes of storing and/or transmitting the tone mapping data.